Rust 编程语言-6-枚举和模式匹配

6. Enum和Pattern matching

6.1 Enum枚举

IP地址枚举

enum IpAddr {
        V4(String),
        V6(String),
}

消息类型枚举：可以看到枚举中每个元素的类型可以不同

enum Message {
    Quit,
    Move { x: i32, y: i32 },
    Write(String),
    ChangeColor(i32, i32, i32),
}

Option枚举

enum Option<T> {
    None,
    Some(T),
}

Option 的使用example

let some_number = Some(5);
let some_string = Some("a string");
let absent_number: Option<i32> = None;

6.2 模式匹配

enum Coin {
    Penny,
    Nickel,
    Dime,
    Quarter,
}

fn value_in_cents(coin: Coin) -> u8 {
    match coin {  //此处有点像Java中的switch
        Coin::Penny => 1,
        Coin::Nickel => 5,
        Coin::Dime => 10,
        Coin::Quarter => 25,
    }
}
fn main() {}

=> : curly brackets

fn plus_one(x: Option<i32>) -> Option<i32> {
        match x {
            None => None,
            Some(i) => Some(i + 1),
        }
    }

_ 下划线代表剩下的所有case

    let dice_roll = 9;
    match dice_roll {
        3 => add_fancy_hat(),
        7 => remove_fancy_hat(),
        _ => (),
    }

    fn add_fancy_hat() {}
    fn remove_fancy_hat() {}

if let的使用

    let config_max = Some(3u8);
    if let Some(max) = config_max {
        println!("The maximum is configured to be {}", max);
    }